Ultrasonic welding devices for welding plastic polymers are well known. Such ultrasonic welders typically comprise a power supply, control electronics, ultrasonic transducer, horn, anvil, and mechanical actuating system mounted to a common frame and/or enclosed in a common housing.
The power supply provides electrical power to the ultrasonic transducer which converts the electric power into high frequency or ultrasonic mechanical vibration which is transferred through the horn to a workpiece. The workpiece is captured between the horn and an anvil to maximize the transfer of ultrasonic energy at the desired workpiece location. The ultrasonic energy transmitted mechanically from the transducer through the horn to the workpiece excites molecular motion within the workpiece, thereby increasing the temperature of the workpiece sufficiently to create a weld upon the workpiece between the horn and anvil.
Such ultrasonic welding apparatus are typically several feet tall and have a footprint of approximately two square feet. They commonly weigh in excess of one hundred pounds. Thus, such prior art ultrasonic welding apparatus cannot be easily moved from location to location or hand held and positioned upon a large workpiece for welding.
Alternative means of attaching plastic parts for large, awkward, or odd-shaped workpieces must be found when such workpieces cannot be accommodated by contemporary ultrasonic welding apparatus. Such alternative attachment means comprise rivets, chemical adhesives, and conventional fasteners such as screws, bolts, and nuts. Such alternative fastening means generally provide less than satisfactory results and are therefore undesirable. For example, mechanical fasteners such as rivets, screws, and nuts and bolts are subject to improper installation and failure. They are also considerably more expensive than ultrasonic welding. Chemical adhesives are subject to improper mix, poor installation, and failure during use. Chemical adhesives are difficult to apply and expensive, thus increasing assembly costs.
A common problem which occurs when attempts are made to use contemporary ultrasonic welding apparatus upon large, awkward or odd-shaped workpieces is the occurrence of weld voids. Weld voids occur when intimate contact of the workpiece is not achieved by the horn and anvil. While it is known in the art that the use of variously shaped anvils can reduce or eliminate weld voids, it is not always practical to change anvils many times when welding a particular workpiece.
Attempts to compensate for the use of an anvil having a less-than-ideal shape are made by striving to angle the workpiece in relation to the ultrasonic welding apparatus such that an adequate contact is achieved. To form a weld within a curved or bent portion of the workpiece, it is normally necessary to use an anvil having a corresponding curve. Rather than take the time to install the correct anvil, many operators attempt to orient the workpiece such that the anvil achieves adequate contact with the workpiece. For example, the length of the anvil could be aligned along the axis of the bend to provide maximum contact.
Minimum contact would be achieved by placing the anvil across the bend such that the anvil only contacts the workpiece at the ends of the anvil. This would result in the formation of a void during welding and should therefore be avoided. The ultrasonic welding of large, awkward, or odd-shaped workpieces makes it extremely difficult to optimize the angle and orientation of the workpiece, thereby requiring that the correct anvil be utilized.
Ultrasonic welding is typically limited to workpieces which can be hand held or mechanically positioned for welding. Thus, very large, awkward, or odd-shaped workpieces are typically unsuitable for ultrasonic welding using contemporary apparatus. Although such contemporary ultrasonic welding apparatus have proven generally suitable for their intended purpose, they possess inherent deficiencies which detract from their overall effectiveness in the marketplace.
In view of the shortcomings of the prior art, it is desirable to provide a portable ultrasonic welding device for performing ultrasonic welding upon large, awkward, or odd-shaped workpieces.
As such, although the prior art has recognized to a limited extent the problem of performing ultrasonic welding upon large, awkward, or odd-shaped workpieces, the proposed solutions have to date been ineffective in providing a satisfactory remedy.